Net::OpenSSH - Perl SSH client package implemented on top of OpenSSH
use Net::OpenSSH; my $ssh = Net::OpenSSH->new($host); $ssh->error and die "Couldn't establish SSH connection: ". $ssh->error; $ssh->system("ls /tmp") == 0 or die "remote system command failed with code: " . ($? >> 8); my @ls = $ssh->capture("ls"); $ssh->error and die "remote ls command failed: " . $ssh->error; my ($out, $err) = $ssh->capture2("find /root"); my ($rin, $pid) = $ssh->pipe_in("cat >/tmp/foo") or die "pipe_in method failed: " . $ssh->error; print $rin, "hello\n"; close $rin; my ($rout, $pid) = $ssh->pipe_out("cat /tmp/foo") or die "pipe_out method failed: " . $ssh->error; while (<$rout>) { print } close $rout; my ($in, $out ,$pid) = $ssh->open2("foo"); my ($pty, $pid) = $ssh->open2pty("foo"); my ($in, $out, $err, $pid) = $ssh->open3("foo"); my ($pty, $err, $pid) = $ssh->open3pty("login"); my $sftp = $ssh->sftp(); $sftp->error and die "SFTP failed: " . $sftp->error;
Net::OpenSSH is a secure shell client package implemented on top of OpenSSH binary client (ssh).
ssh
This package is implemented around the multiplexing feature found in later versions of OpenSSH. That feature allows reuse of a previous SSH connection for running new commands (I believe that OpenSSH 4.1 is the first one to provide all the required functionality).
When a new Net::OpenSSH object is created, the OpenSSH ssh client is run in master mode, establishing a permanent (actually, for the lifetime of the object) connection to the server.
Then, every time a new operation is requested a new ssh process is started in slave mode, effectively reusing the master SSH connection to send the request to the remote side.
Why should you use Net::OpenSSH instead of any of the other Perl SSH clients available?
Well, this is my (biased) opinion:
Net::SSH::Perl is not well maintained nowadays, requires a bunch of modules (some of them very difficult to install) to be acceptably efficient and has an API that is limited in some ways.
Net::SSH2 is much better than Net::SSH::Perl, but not completely stable yet. It can be very difficult to install on some specific operative systems and its API is also limited, in the same way as Net::SSH::Perl.
Using Net::SSH::Expect, in general, is a bad idea. Handling interaction with a shell via Expect in a generic way just can not be reliably done.
Net::SSH is just a wrapper around any SSH binary commands available on the machine. It can be very slow as they establish a new SSH connection for every operation performed.
In comparison, Net::OpenSSH is a pure perl module that doesn't have any mandatory dependencies (obviously, besides requiring OpenSSH binaries).
Net::OpenSSH has a very perlish interface. Most operations are performed in a fashion very similar to that of the Perl builtins and common modules (i.e. IPC::Open2).
It is also very fast. The overhead introduced by launching a new ssh process for every operation is not appreciable (at least on my Linux box). The bottleneck is the latency intrinsic to the protocol, so Net::OpenSSH is probably as fast as an SSH client can be.
Being based on OpenSSH is also an advantage: a proved, stable, secure (to paranoic levels), interoperable and well maintained implementation of the SSH protocol is used.
On the other hand, Net::OpenSSH does not work on Windows.
Net::OpenSSH specifically requires the OpenSSH SSH client (AFAIK, the multiplexing feature is not available from any other SSH client). However, note that it will interact with any server software, not just servers running OpenSSH sshd.
sshd
For password authentication, IO::Pty has to be installed. Other modules and binaries are also required to implement specific functionality (for instance Net::SFTP::Foreign, Expect or rsync(1)).
Several of the methods in this package accept as first argument an optional reference to a hash containing parameters (\%opts). For instance, these two method calls are equivalent:
\%opts
my $out1 = $ssh->capture(@cmd); my $out2 = $ssh->capture({}, @cmd);
Most methods return undef (or an empty list) to indicate failure.
The error method can always be used to explicitly check for errors. For instace:
error
my ($output, $errput) = $ssh->capture2({timeout => 1}, "find /"); $ssh->error and die "ssh failed: " . $ssh->error;
These are the methods provided by the package:
*** Note that this is an early release, the *** *** module API has not yet stabilized!!! ***
Creates a new SSH master connection
$host can be a hostname or an IP address. It may also contain the name of the user, her password and the TCP port number where the server is listening:
$host
my $ssh1 = Net::OpenSSH->new('jack@foo.bar.com'); my $ssh2 = Net::OpenSSH->new('jack:secret@foo.bar.com:10022');
This method always succeeds in returning a new object. Error checking has to be performed explicitly afterwards:
my $ssh = Net::OpenSSH->new($host, %opts); $ssh->error and die "Can't ssh to $host: " . $ssh->error;
Accepted options:
Login name
TCP port number where the server is running
User password for logins on the remote side
Note that using password authentication in automated scripts is a very bad idea. When possible, you should use public key authentication instead.
Directory where the SSH master control socket will be created.
This directory and its parents must be writable only by the current effective user or root, otherwise the connection will be aborted to avoid insecure operation.
By default ~/.libnet-openssh-perl is used.
~/.libnet-openssh-perl
Name or full path to OpenSSH ssh binary. For instance:
my $ssh = Net::OpenSSH->new($host, ssh_cmd => '/opt/OpenSSH/bin/ssh');
Name or full path to OpenSSH scp binary.
scp
By default it is inferred from the ssh one.
Name or full path to rsync binary. Defaults to rsync.
rsync
<aximum acceptable time that can elapse without network traffic or any other event happening on methods that are not immediate (for instance, when establishing the master SSH connection or inside capture method).
capture
By default, the connection will be aborted if the path to the socket used for multiplexing is found to be non-secure (for instance, when any of the parent directories is writable by other users).
This option can be used to disable that feature. Use with care!!!
By default, the constructor waits until the multiplexing socket is available. That option can be used to defer the waiting until the socket is actually used.
For instance, the following code connects to several remote machines in parallel:
my (%ssh, %ls); for my $host (@hosts) { $ssh{$host} = Net::OpenSSH->new($host, async => 1); } for my $host (@hosts) { $ssh{$host}->system('ls /'); } }
Additional options to pass to the ssh command when establishing the master connection. For instance:
my $ssh = Net::OpenSSH->new($host, master_opts => [-o => "ProxyCommand corkscrew httpproxy 8080 $host"]);
Default I/O streams for open_ex and derived methods (currently, that means any method but system, pipe_in and pipe_out and I plan to remove those exceptions soon!).
system
pipe_in
pipe_out
For instance:
open my $stderr_fh, '>>', '/tmp/$host.err' or die ...; open my $stdout_fh, '>>', '/tmp/$host.log' or die ...; my $ssh = Net::OpenSSH->new($host, default_stderr_fh => $stderr_fh, default_stdout_fh => $stdout_fh); $ssh->error and die "SSH connection failed: " . $ssh->error; $ssh->scp_put("/foo/bar*", "/tmp") or die "scp failed: " . $ssh->error;
Returns the error condition for the last performed operation.
The returned value is a dualvar as $! (see "$!" in perlvar) that renders an informative message when used in string context or an error number in numeric context (error codes appear in Net::OpenSSH::Constants).
Return the corresponding SSH login parameters.
Similar to the system builtin, runs the command @cmd on the remote machine using the current stdin, stdout and stderr streams for IO.
@cmd
Example:
$ssh->system('ls -R /');
The value returned also follows the system builtin convention (see "$?" in perlvar).
That method starts the command @cmd on the remote machine creating new pipes for the IO channels as specified on the %opts hash.
%opts
Returns four values, the first three correspond to the local side of the pipes created (they can be undef) and the fourth to the PID of the new SSH slave process. An empty list is returned on failure.
Note that waitpid has to be used afterwards to reap the slave SSH process.
waitpid
Creates a new pipe and connects the reading side to the stdin stream of the remote process. The writing side is returned as the first value.
Similar to stdin_pipe, but instead of a regular pipe it uses a pseudo-tty (pty).
stdin_pipe
Note that on some OSs (i.e. HP-UX, AIX), ttys are not reliable. They can overflow when large chunks are written or when data is written faster than it is read.
Duplicates $fh and uses it as the stdin stream of the remote process.
$fh
Creates a new pipe and connects the writting side to the stdout stream of the remote process. The reading side is returned as the second value.
Connects the stdout stream of the remote process to the pseudo-pty. This option requires stdin_pty to be also set.
stdin_pty
Duplicates $fh and uses it as the stdout stream of the remote process.
Creates a new pipe and connects the writting side to the stderr stream of the remote process. The reading side is returned as the third value.
Duplicates $fh and uses it as the stderr stream of the remote process.
Makes stderr point to stdout.
Tells the remote process that it is connected to a tty.
When a pseudo pty is used for the stdin stream, the slave side is automatically closed on the parent process after forking the ssh command.
This option dissables that feature, so that the slave pty can be accessed on the parent process as <$pty-slave>>. It will have to be explicitly closed (see IO::Pty)
<$pty-
See "Shell quoting" below.
Usage example:
# similar to IPC::Open2 open2 function: my ($in_pipe, $out_pipe, undef, $pid) = $ssh->open_ex( { stdin_pipe => 1, stdout_pipe => 1 }, @cmd ) or die "open_ex failed: " . $ssh->error; # do some IO through $in/$out # ... waitpid($pid);
This method is similar to the following Perl open call
open
$pid = open $in, '|-', @cmd
but running @cmd on the remote machine (see "open" in perlfunc).
No options are currently accepted.
There is no need to perform a waitpid on the returned PID as it will be done automatically by perl when $in is closed.
$in
my ($in, $pid) = $ssh->pipe_in('cat >/tmp/fpp') or die "pipe_in failed: " . $ssh->error; print $in $_ for @data; close $in or die "close failed";
Reciprocal to previous method, it is equivalent to
$pid = open $out, '-|', @cmd
running @cmd on the remote machine.
Shortcuts around open_ex method.
open_ex
Another open_ex shortcut, it launches a new remote process in the background and returns its PID.
For instance, you can run some command on several host in parallel with the following code:
my %conn = map { $_ => Net::OpenSSH->new($_) } @hosts; my @pid; for my $host (@hosts) { open my($fh), '>', "/tmp/out-$host.txt" or die "unable to create file: $!; push @pid, $conn{$host}->spawn({stdout_fh => $fh}, $cmd); } waitpid($_, 0) for @pid;
This method is conceptually equivalent to the perl backquote operator (i.e. `ls`): it runs the command on the remote machine and captures its output.
`ls`
In scalar context returns the output as a scalar. In list context returns the output broken into lines (it honors $/, see "$/" in perlvar).
$/
When an error happens while capturing (for instance, the operation times out), the partial captured output will be returned. Error conditions have to be explicitly checked using the error method. For instance:
my $output = $ssh->capture({ timeout => 10 }, "echo hello; sleep 20; echo bye"); $ssh->error and warn "operation didn't complete successfully: ". $ssh->error; print $output;
Redirect stderr to stdout. Both streams will be captured on the same scalar interleaved.
Attaches the remote command stderr stream to the given file handle.
Sends the given data to the stdin stream while capturing the output on stdout.
Attaches the remote command stdin stream to the given file handle.
The operation is aborted after $timeout seconds elapsed without network activity.
$timeout
As the Secure Shell protocol does not support signalling remote processes, in order to abort the remote process its input and output channels are closed. Unfortunately this aproach does not work in some cases.
captures the output sent to both stdout and stderr by @cmd on the remote machine.
The accepted options are:
sends the given data to the stdin stream while simultaneously captures the output on stdout and stderr.
attachs the remote command stdin stream to the given file handle.
The operation is aborted after $timeout seconds elapse without network activity.
These two methods are wrappers around the scp command that allow transfers of files to/from the remote host using the existing SSH master connection.
When transferring several files, the target argument must point to an existing directory. If only one file is to be transferred, the target argument can be a directory or a file name or can be ommited. For instance:
$ssh->scp_get({glob => 1}, '/var/tmp/foo*', '/var/tmp/bar*', '/tmp'); $ssh->scp_put('/etc/passwd');
Both scp_get and scp_put methods return a true value when all the files are transferred correctly, otherwise they return undef.
scp_get
scp_put
By default, scp is called with the quiet flag -q enabled in order to suppress progress information. This option allows reenabling the progress indication bar.
-q
Copy files and directories recursively.
Allow expansion of shell metacharacters in the sources list so that wildcards can be used to select files.
Second argument passed to File::Glob bsd_glob function. Only available for scp_put method.
bsd_glob
Copies modification and access times and modes from the original files.
Limits the used bandwith, specified in Kbit/s.
Doesn't wait for the scp command to finish. When this option is used, the method returns the PID of the child scp process.
For instance, it is possible to transfer files to several hosts in parallel as follows:
use Errno; my (%pid, %ssh); for my $host (@hosts) { $ssh{$host} = Net::OpenSSH->new($host, async => 1); } for my $host (@hosts) { $pid{$host} = $ssh{$host}->scp_put({async => 1}, $local_fn, $remote_fn) or warn "scp_put to $host failed: " . $ssh{$host}->error . "\n"; } for my $host (@hosts) { if (my $pid = $pid{$host}) { if (waitpit($pid, 0) > 0) { my $exit = ($? >> 8); $exit and warn "transfer of file to $host failed ($exit)\n"; } else { redo if ($! == EINTR); warn "waitpid($pid) failed: $!\n"; } } }
These options are passed unchanged to method open_ex, allowing capture of the output of the scp program.
Note that scp will not generate progress reports unless its stdout stream is attached to a tty.
These methods use rsync over SSH to transfer files from/to the remote machine.
They accept the same set of options as the SCP ones.
Any unrecognized option will be passed as an argument to the rsync command. Underscores can be used instead of dashes in rsync option names.
$ssh->rsync_get({exclude => '*~', verbose => 1, safe_links => 1}, '/remote/dir', '/local/dir');
Creates a new Net::SFTP::Foreign object for SFTP interaction that runs through the ssh master connection.
When the connection has been established by calling the constructor with the async option, this call allows to advance the process.
async
If $async is true, it will perform any work that can be done inmediately without waiting (for instance, entering the password or checking for the existence of the multiplexing socket) and then return. If a false value is given, it will finalize the connection process and wait until the multiplexing socket is available.
$async
It returns a true value after the connection has been succesfully established. False is returned if the connection process fails or if it has not yet completed ($ssh->error can be used to distinguish between those cases).
$ssh->error
Returns the list of arguments quoted so that they will be restored to their original form when parsed by the remote shell.
Usually this task is done automatically by the module. See "Shell quoting" below.
This method is like the previous shell_quote but leaves wildcard characters unquoted.
shell_quote
Returns the path to the socket where OpenSSH listens for new multiplexed connections.
By default, when invoking remote commands, this module tries to mimic perl system builtin in regard to argument processing. Quoting "system" in perlfunc:
Argument processing varies depending on the number of arguments. If there is more than one argument in LIST, or if LIST is an array with more than one value, starts the program given by the first element of the list with arguments given by the rest of the list. If there is only one scalar argument, the argument is checked for shell metacharacters, and if there are any, the entire argument is passed to the system's command shell for parsing (this is "/bin/sh -c" on Unix platforms, but varies on other platforms).
Take for example Net::OpenSSH system method:
$ssh->system("ls -l *"); $ssh->system('ls', '-l', '/');
The first call passes the argument unchanged to ssh, so that it is executed in the remote side through the shell which interprets shell metacharacters.
The second call escapes especial shell characters so that, effectively, it is equivalent to calling the command directly and not through the shell.
Under the hood, as the Secure Shell protocol does not provide for this mode of operation and always spawns a new shell where it runs the given command, Net::OpenSSH quotes any shell metacharacters in the comand list.
All the methods that invoke a remote command (system, open_ex, etc.) accept the option quote_args that allows to force/disable shell quoting.
quote_args
$ssh->system({quote_args => 1}, "/path with spaces/bin/foo");
will correctly handle the spaces in the program path.
The option quote_args can also be used to disable quoting when more than one argument is passed. For instance, to get some pattern expanded by the remote shell:
$ssh->system({quote_args => 0}, 'ls', '-l', "/tmp/files_*.dat");
The method shell_quote can be used to selectively quote some arguments and leave others untouched:
$ssh->system({quote_args => 0}, $ssh->shell_quote('ls', '-l'), "/tmp/files_*.dat");
When the glob option is set in scp and rsync file transfer methods, an alternative quoting method that knows about file wildcards and passes them unquoted is used. The set of wildcards recognized currently is the one supported by bash(1).
As shell quoting is a tricky matter, I expect bugs to appear in this area. You can see how ssh is called, and the quoting used setting the corresponding debug flag:
$Net::OpenSSH::debug |= 16;
Question: I use $ssh->spawn to asyncronously run compile jobs on slave machines. The Net::OpenSSH objects where compilation failed does not show error with $ssh->error. Is $ssh->error supposed to work in this case?
$ssh->spawn
Answer: $ssh->error is only about the SSH layer. Exit codes for the remote commands are available in $? (see "system" in perlfunc and perlipc).
$?
my $pid = $ssh->spawn('gcc test.c'); $ssh->error and die "unable to start compilation job: ". $ssh->error; ... waitpid($pid, 0); my $exit = ($? >> 8); $exit == 0 or die "compilation failed with code $exit";
OpenSSH client documentation: ssh(1), ssh_config(5).
Core perl documentation perlipc, "open" in perlfunc, "waitpid" in perlfunc.
IO::Pty to known how to use the pseudo tty objects returned by several methods on this package.
Net::SFTP::Foreign provides a compatible SFTP implementation.
Expect can be used to interact with commands run through this module on the remote machine.
Other Perl SSH clients: Net::SSH::Perl, Net::SSH2, Net::SSH, Net::SSH::Perl.
SCP and rsync file transfer support is still highly experimental.
Does not work on Windows. OpenSSH multiplexing feature requires passing file handles through sockets but that is not supported by Windows.
Doesn't work on VMS either... well, actually, it probably doesn't work on anything not resembling a modern Linux/Unix OS.
Tested on Linux and NetBSD with OpenSSH 5.1p1
To report bugs send my an email to the address that appear below or use the CPAN bug tracking system.
For questions related to module usage, you can also contact my by email but I would prefer if you post them in PerlMonks (that I read frequently), so other people can also find them.
- add expect method
- passphrase handling
- integrate with IPC::PerlSSH
- better timeout handling in capture methods
- add support for more target OSs (quoting, OpenVMS, Windows & others)
- add tests for scp and rsync methods
- make pipe_in, pipe_out and system methods open_ex based
- write some kind of parallel queue manager module
Send your feature requests, ideas or any feedback, please!
Copyright (C) 2008, 2009 by Salvador Fandiño (sfandino@yahoo.com)
This library is free software; you can redistribute it and/or modify it under the same terms as Perl itself, either Perl version 5.10.0 or, at your option, any later version of Perl 5 you may have available.
To install Net::OpenSSH, copy and paste the appropriate command in to your terminal.
cpanm
cpanm Net::OpenSSH
CPAN shell
perl -MCPAN -e shell install Net::OpenSSH
For more information on module installation, please visit the detailed CPAN module installation guide.